The levogyre ascorbic acid, hereinafter called LAA, presents the following formula: ##STR1## and is an element known since long ago in the pharmacopeia, in medicine and in the cosmetic industry. Its application aims at the most varied benefits, from the treatment of stomachal problems, regeneration of skin signs hygienization and attenuation of skin marks. The expression "skin signs" as used herein means the signs of skin aging, such as wrinkles resulting from the action of time and from external factors such as climatic actions (sunshine, wind and temperature).
Examples of the employ of LAA in medicine are described in U.S. Pat. No. 2,132,662, granted in November, 1938 to Abbott Laboratories, the inventors of which are Ernst H. Volwiler and others, in this case as an antiscorbutic agent, and in U.S. Pat. No. 2,721,161, granted in 1955 to the inventor Maise and others, who taught the use of LAA plus a non-ionic surfactant in preparing oral or intravascular compositions for restoring the level of LAA in the blood.
The same is true of the cosmetic industry, where the LAA in molecular form, either associated or not with its salts and esters, has been employed in fighting the cutaneous aging process. In large part, in the segment of cosmetics, the salts and esters of the LAA alone are employed more frequently than the LAA in its molecular form, since the former are chemically more stable, which has been resulting in less effective products than the case would have been if the LAA in its molecular form had been used.
As to the form of action intended by the cosmetics industry for fighting cutaneous aging, be it by using the LAA or its derivatives, studies carried out by the applicant and the literature show that skin aging comprises a regressive phase of the life cycle with anatomic and physiological alterations, with degradation of certain organs and tissues.
Some literature references which incorporate the studies made by the applicant include: 1- DARR, D.; COMBS, S.; PINNELL, S. Ascorbic acid and collagen synthesis: Rethinking a role for lipid peroxidation. Archives of Biochemistry and Biophysics. 307, 331-5, 1993; 2- PINNEL, S. ; MURAD, S. Vitamin C and collagen metabolism. In: KLIGMAN, A. M.; TAKASE, Y., Cutaneous aging Du University Medical Cancer, 275-92, 1988; 3- PINNELL S. Vitamina C topica (Topical Vitamin C). Revista de Cosmiatria & Medicina Estetica. 31-6, 4o. trim 1995; 4- DARR, D.; COMBS, S.; DUNSTON, S.; MANNING, T.; PINNEL, S. Topical Vitamin C protects porcine skin from ultraviolet radiation-induced damage. British Journal of Dermatology. 127, 247-53, 1992; 5- PINNELL, S. Regulation of collagen biosynthesis by ascorbic acid: a review. The Yale Journal of Biology and Medicine, 58, 553-9, 1985.
The aging manifests itself on the skin by the loss of elasticity, loss of turgency, formation of wrinkles and the appearance of stains. Among the physiological alterations which actively contribute to this process, we can mention decrease in immunological functions, decline of basal metabolism, alterations in the structure of the conjunctive tissue, decrease in the capability of renewing the cutaneous lipids and in the hygroscopic components, leading to a lesser power of hydric retention and, consequently, to dehydration of the skin.
All of these alterations are the reflex of a series of internal and external factors which jointly contribute to the aging process.
As internal factors, directly controlled by the genetic patterns of the individual, the following can be cited: the chronological factor, defined by the aging, influenced by the genetic information contained in the cells; the immunological factor, given by the decrease of the Langerhans cells, responsible for the immunity vigilance of the skin; the hormonal factor, given by the decrease of the hormonal activity, especially of androgenic hormones, impairing the capability of hydric retention of the epidermis.
Interacting with the internal factors, a series of external factors too modulate the cutaneous aging, such as the photoaging, caused by the UV-A and UV-B radiations. The ultraviolet radiation acts at intercellular levels, inducing alterations in the DNA capable of forming incorrect proteins and enzymes, accelerating and altering the activities of cells. At the extracellular level, it may cause structural alterations in the collagen and elastin fibers and in the proteoglycans, which are fundamental in maintaining the turgor and the structure of the dermic layer. These alterations form groups of amorphous mass, which cause a lowering in the outer surface of the skin, also known as wrinkles. In addition to these damages, the UV radiation also promotes reactions of the molecular oxygen with lipids and proteins of the cellular membranes (lipoperoxidation), forming free radicals, which are molecules extremely dangerous to the cells.
In addition, one can point out as external factors the so-called Environmental Factors, for example, excessively low or high temperatures, wind, low relative moisture of the air and pollution, which in turn attack the protecting hydrolipidic mantle, leading to the loss of transepidermal, water with the consequent dehydration of the skin. There are equally the Emotional Factors and the Living Habits, generally stressing in the big cities and characterized by poor alimentation, smoking and drinking, which cause either alterations or unbalances in the metabolism of the lipids and proteins of the dermic layer.
These factors affect the skin in some way and can be enhanced by the age of the individual or by the biological cycle.
The biological cycles of an individual are constituted by a set of alterations resulting from these external and internal factors already described. The way in which each cycle has been lived by the individual will result in the degree of alterations.
The cutaneous aging can be divided into 3 main cycles: the first one begins at the age of 30, the second one comprises the range from 45 to 60 years of age, and the third one from the age of 60 on.
In the age group of from 30 to 45 the skin, in general, does not present any visible marks. The action of the free radicals decreases the activity of cells involved in the immunological responses. Every 10 years the skin loses 10% of this defence mechanism. Collagen and elastin, damaged by the UV radiation, have their restoration decreased. Natural aging and the action of free radicals are also responsible for this reduction.
Between 45 and 60 years of age, there is a drop in the production of tallow by the sebaceous glands, due to the lesser concentration of androgenic hormones. The signs of weakening of the circulatory system become more evident. The damages caused by free radicals intensify and the deficiencies of the immune system become more accented, in addition to a decrease in efficiency of the fibroblasts, impairing the restoration of collagen. There is also a reduction in the production of elastic fibers and of glucosaminoglycans, leading to the loss of sustainment.
From 60 years of age on, the signs which began in the preceding cycle become more accented. The sebaceous glands are virtually destroyed, because they receive less androgenic stimulus and the deficient circulatory picture becomes accented, thus decreasing the nutritional contribution and the elimination of toxins. An increase in the immunologic deficiency is noted, especially in the areas which are exposed to UV radiation, and the wrinkles become accented with an increase in seriousness of the previously described picture, due to the drop in production of collagen, elastin and glucosaminoglycans.
The technologies for treatment of the skin have tried to treat not only the visible signs of aging, but also to actuate more and more deeply on the causes thereof, by preventing potential risks which might contribute to the aging process. On this basis, the active principles are developed for actuating at specific sites of action, acting directly where they are required, that is to say, in deeper layers of the skin and directly on the aspects which guarantee the cutaneous sustainment.
The LAA has been one of the most researched elements for this purpose, the main focus being the obtention of its stabilization, since it is one of the main antioxidants existing in our blood and in other fluids of the tissues.
Just as the body, the skin too grows old. Many of the unwanted effects of the cutaneous aging (such as wrinkles) can be attributed to the loss of connective tissue. With the aging the dermis becomes thinner and over 20% of its thickness is lost.
The LAA plays a vital role in the growth and repair of connective tissue. Many studies have proven its action in the process of cellular regeneration and skin protection, by a series of mechanisms. The LAA is directly involved in the stimulation of the biosynthesis of collagen, a macromolecule that is fundamental for maintaining the tonus of the skin. As an antioxidant substance, it fights directly the free radicals, which are elements connected with the cutaneous aging (an action proved by studies "in vitro"). Besides, the LAA is capable of protecting the skin against UV radiation and its subsequent damages.
Scientific reports show that the skin, especially with the aging, becomes deficient in LAA.
The amount of LAA supplied by the alimentation is not sufficient to actuate on the skin effectively and to fight the damages of the aging process. The LAA, via ingestion of food or by oral supplementation, is distributed throughout the organism and, depending on the needs of the latter, may not reach the skin in quantities sufficient to stimulate the synthesis of collagen, and to fight free radicals. In this way, under limit conditions of ascorbic acid, the latter can be absorbed and used preferably to maintain the more vital needs of the organism, to the detriment of the supply in the cutaneous tissue.
Higher levels of LAA in the skin cannot be obtained orally alone. Studies with topical applications of LAA indicate that it reaches pharmacological levels much higher than those found in normal skin. In this way, by topical use, it is possible to reach ideal concentrations of LAA, so that it can act efficiently and directly as an antioxidant, antiphologistic and regenerative agent.
Collagen, the most abundant protein of the skin and fundamental for maintaining the tonus of the skin, is regulated in every step of its synthesis.
The LAA is essential in the biosynthesis of collagen, actuating as an important cofactor of its fundamental enzymes: prolylhydroxylase and lysylhydroxylase, which actuate converting proline into hydroxyproline (an aminoacid that is fundamental to the stability of the triple helix of procollagen) and in converting lysin into hydroxylysin (another aminoacid that is fundamental to the stabilization of the structure of collagen, participating in the formation of intermolecular links and imparting mechanical stability to the fiber).
Independently of its participation in the hydroxylation of lysin and proline, the LAA can have an additional effect on the biosynthesis of collagen by genetic regulation, promoting an inducing effect in the synthesis of collagen upon stimulating the genic transcription for collagens of type I and type III. Studies "in vitro" with human fibroblasts show an increase in the synthesis of mRNA of 2 to 3 times as high, when in the presence of LAA. These mRNA also prove to be about 2 times as efficient in the translation of the polypeptidic chains of collagen, without causing any alteration in the process of synthesis of non-collagenic proteins.
There is also the action of the LAA on the production of glucosaminoglycines, components of the extracellular matrix of the dermis, closely related to the collagen fibers. In the presence of LAA, their synthesis can be increased from 30 to 90%, with 50% of increase in their deposition in the extracellular matrix.
The LAA is also one of the main biological antioxidants, by virtue of its reducing properties, being capable of neutralizing these highly reactive species, important figures in the aging process. It can also act an antioxidant in the peroxidative processes of metabolization of fats and formation of free radicals, besides contributing to maintain vitamin E in the organism, also an important antioxidant, in its reduced form, assisting in the protection against lipoperoxidation and, consequently, avoiding injury to the cellular membranes. It should be stressed that qualitatively, the antiradical action of the LAA is superior to that of Vitamin E and Glutation, even if associated.
The damages to the skin produced by ultraviolet radiation are due, in part, to the generation of certain varieties of reactive oxygen, as the superoxide anion, the singlet oxygen and the hydroxyl radical. The oxidative aggression promoted by the radication with generation of free radicals results in generalized damages to the constituents of the skin.
As a result of exposition to the sunshine, the dermis undergoes major alterations, accenting the normal process of cutaneous aging. In this case, we have the degeneration of the elastic material, degeneration of the collagen and accumulation of glucosaminoglycans. The fibroblasts, exposed to UV radiation, reduce or even lose their capacity of synthesis of macromolecules of sustainment.
The LAA in topical use is capable of protecting the skin against UVA and UVB radiations. However, it does not actuate as a sun filter, since it is not capable of absorbing radiation in this spectrum. Its protecting effect is directly connected to its antiradical action. Its role as an antioxidant is essential to protect the skin against oxidative damages produced by exposition to radiation and to the inflammatory reaction associated thereto.
The LAA cannot be synthesized by the human body, but it is available in vegetables and mainly in citric fruits. Pure LAA, either extracted from fruits or chemically synthesized, is a white or slightly yellowish powder, which has a relative stability when dissolved in an aqueous medium. This compound is easily oxidable in the presence of atmospheric air, changing into dehydro ascorbic acid, in addition to other products resulting from the oxidation. Such a transformation decreases its physiological properties, principally in the use conditions in which there is exposition of the compound to atmospheric air, as for instance, when using a topical solution.
In a simplified way, the instability of LAA manifests itself by the fact that, when dissolved in an aqueous medium, it becomes ionized, forming LAA anions and releasing H+ ions.
Due to this instability, although it shows greater efficiency when in its original form, that is to say, in its molecular formula, the LAA is used in the form of its salts or esters, so that the resulting compositions have greater stability for long periods of time, thus preventing degradation due to contact with the oxygen dissolved in water and absorbed from atmospheric air.
However, many works have been carried out for the main purpose of achieving stability of the LAA in its molecular form, in order to enable its use in medicaments and cosmetic compositions. An example of this approach can be found in U.S. Pat. No. 4,983,382 of Jan. 8, 1991. According to this patent, a solution containing LAA would become stable by its being added to an organic solution comprising a first co-solvent, water up to 12% by weight and a second co-solvent in a concentration of up to 90%, based on the total weight of the solution and further containing, compulsorily, ethanol in a concentration of at least 40% by weight of the solution.
The disadvantage of this type of organic solution for the cosmetic and pharmaceutical industry or food industry consists in the fact, even though it can exhibit an acceptable stability of the LAA, the addition of ethanol in the mentioned contents causes the skin to become irritated and very dry, which may render the permeation of the LAA by corneous extract difficult, besides, of course, causing an unpleasant feeling to the user.
Another use of the LAA in its molecular form is described in Brazilian patent application PI 9008018, filed in the name of Bioderm, Inc. This document refers to a composition for reducing the depth or intensity of fine wrinkles on a skin affected by intrinsic or photoinduced aging. Although it does not make detailed comments about the stability of the LAA, the referred-to patent application describes a series of actions that are beneficial in the reduction of the depth or intensity of fine wrinkles by the use of a topical formulation which comprises, in combination with the LAA, tyrosine and a zinc salt such as zinc sulphate, and can be formulated either as a salve or as a hydrophilic cream. The compulsory inclusion of tyrosine and a zinc salt makes the solution more expensive for the consumer, because of the great number of ingredients for its production, and its effective action in fighting the cutaneous aging has not been totally proved yet.
In more recent works for achieving stability of the LAA in its molecular form, the objective was to avoid the degradation of the acid by maintaining the pH at low levels. In these works the appearance of ascorbates to the detriment of the maintenance of molecular LAA in the solution was credited to the occurrence of ionization of the LAA and its degradation due to the contact of the LAA-anion with oxygen (either atmospheric air or pure oxygen present in the solution).
In fact, the ionization of the LAA causes the formation of an ascorbate (LAA-), which is a metastable structure in water due to the electronic resonance between the carbons 1, 2, and 3 of the LAA, and the release of H+ions. ##STR2##
This reaction is governed by the spontaneousness (free energy or "DeltaG&lt;0") of the LAA for ionizing until a dynamic balance between the reactants (LAA) and the products (LAA-+H+) is reached, and it can be represented as follows: EQU LAA&lt;-&gt;LAA-+H+.
In order for the minimum amount of ascorbate to be formed as a product of ionization and, therefore, for the maximum of LAA to remain stable, it was believed that the pH of the solution should be as low as possible. For this purpose, the practice common to various earlier solutions was to add any acid whatever as a citric acid, for instance, or to increase the initial concentration of LAA.
The pH of such a solution containing LAA was related to the concentration of LAA by the following equation: EQU pH=pK1+log((LAA)/(LAA-))
wherein pH indicates the degree of acidity of the solution; pK1 is the first constant of ionization of the LAA, equal to 4.2; (LAA) is the concentration of LAA in its molecular form, contained in the solution; and (LAA-) is the concentration of ascorbate contained in the solution.
Thus, by the above equation, read according to the knowledge from the prior art, in order for the biggest possible amount of LAA not to ionize (higher stability), the pH value of the solution should be lower than the pK1, a fact which has probably guided most of the solutions known from the prior art. Graphically, this statement can be confirmed by analyzing FIG. 1, which represents a curve of pH versus the molar fraction of the LAA-. In this figure, we can see that for low pH values, we would have high concentrations of LAA and low concentrations of LAA-.
U.S. Pat. No. 5,140,043, granted on Aug. 8, 1992, for instance, teaches that the stabilization of the LAA in amounts higher than 1% by volume of water can be achieved in an aqueous medium, when a carrier for topical application in a water carrier ratio of at least 1:1 is associated to the LAA, the pH of the solution being lower than 3.5. Although this is a mutual association between the LAA contents, the relationship between water and the carrier and a low pH (lower than 3.5), the inventors give a great importance to the pH value in the stability of the LAA, the latter being considered an element guaranteeing that at least 82% of the LAA will remain in its non-modified molecular form, as can be seen from the passage of column 4, lines 7-9, of that document.
One of the disadvantages that are widely discussed by the inventors of that patent is the fact that the carbons 2 and 3 contain acidic hydrogens that are ionizable in water, by virtue of a physical and chemical characteristic of the LAA, that is to say, its ionization constant (pK) equal to 4.2.
In spite of the technical advance provided by that patent, the topical use of a solution as described therein can irritate the more sensitive parts of the skin, such as the contours of the eyes, for example. Since the pH of the human skin is about 4 to 5, this feeling of irritation may be easily attributed to what those inventors considered in the patent to be the "important factor guaranteeing stabilization of the LAA in its molecular form", that is to say, the low pH value of the solution, which is lower than 3.5, preferably lower than 2.5.
In addition, another great disadvantage of the solution disclosed in U.S. Pat. No. 5,140,043 is that, although the stability tests discussed therein are exhaustive, they took into account conditions that are far from the reality of the use of a product intended for topical application and for being handled for a long time. As regards the time of carrying out the test, it took only 12 weeks (84 days) and the low temperatures and luminosity to which the topical solution was exposed are hardly encountered in the home of a consumer or even in a doctor's office. With good chance, the conditions established for those tests would safeguard the topical solution only against the most severe actions of instabilization and degradation of the LAA.
More recently, the publication of patent application EP 670157, filed in the name of L'Oreal, describes the formation of a topical emulsion comprising an aqueous phase dispersed in an oily phase with the help of an emulsifier, dimeticonecopolyol, containing LAA at acidic pH of 3.5, at most. Just as in the case of U.S. Pat. No. 5,140,043, the emulsion described in the referred-to European patent application shows a profile that irritating the skin due to the low pH, which is enhanced by the compulsory inclusion of an artificial emulsifier, which in turn is also irritating.
Therefore, it is an objective of the present invention to provide an effective process for stabilizing LAA in an aqueous medium, which will enable the use of LAA in its molecular form, particularly in cosmetic, pharmaceutical or nutritional aqueous compositions which are stable enough to guarantee the results desired in storing and handling these compositions during cosmetic or therapeutical treatments, without causing damages to the organism of the individuals subjected to these treatments.